Oxidation resistant transformer oils and the like



Patented Mar. 16, 1954 UNETED STATES f AT'EN T OXIDATION RESISTANT TRANSFORMER OILS AND THE LIKE No Drawing. Application August 9, 1949, Serial No. 109,426

"5'Claims. l

F'I'his invention relates to the stabilization of lubricating oil compositions intended for use in the service of transformer oils, turbine oils and the like. More particularly, this invention pertains to mineral oil compositions useful as transformer oils, wherein the anti-oxidation characteristics of the anti-oxidant present in the composition (e. g., selenium compounds) have been enhanced by the presence of Jhydroxyanthraquinone compounds (e. ,g., quinizarin).

For a number of years, it has been the general practice to use moderately treated mineral oils as transformeroils. These moderately treated oils, however, gradually deteriorate in service. This deterioration is normally due to oxidation effects, which eiiects are increased several fold by the presence of the materials (i. e., the brass, copper, silica steel, etc.) of the transformer systems, which materials serve as oxidation catalysts. In turbine oils, the oxidation is catalytically promoted by the copper, lead, steel and. brass which are found in the turbine system.

The effectiveness of a transformer oil as an insulating oil is materially reduced by the oxidation products (1. e., the acid products) formed. Furthermore, these acid products gradually attack the insulation on the wires of the transformer system, leaving the wires partially exposed to the oil, which oil then serves as a transmitter of current instead of an inhibitor of current. In the turbine oils the oxidation products (i. e., the acid sludges) corrode the bearings and other parts of the turbine system and clog the oil lines, etc.

It is a tremendous advantage in transformer, turbine, and like systems, to use the oils of sufiicient oxidation stability to permit their use over long periods of time without being changed. Not only is it desirable to have transformer oils and the like highly resistant to oxidation, but it is also a desired feature of the transformer oils and the like that the viscosity index be high; that is, that only small changes in viscosity occur with large changes in temperature. Thus, in order to obtain oils of high viscosity index, the base oils are subjected to such effective methods of refining as the selective solvent extraction processes wherein the lower viscosity index hydrocarbons are selectively dissolved. These selective solvent refining processes concentrate in one fraction, usually the undissolved oil fraction, those compounds of a parafiinic nature which show a smaller change in viscosity upon change in temperature.

However, highly-refined oils have smaller amounts of the naturally occurringoxidationlinhibitors present in the oils than rdo less refined oils. That is, these naturally occurring inhibitors have been removed at least to an "extent which materially reduces the oxidation "stability of the oil when used as transformer oils and i925 turbine oils.

When oxidation inhibitors are added "to highly refined oils and oils which are'no't so *highly i 'e fined, it is found that the highly refined -oils are more responsive to the oxidation inhibitors that is, when the oxidation inhibitors of this invention are incorporated in so-called nver-refine'd dns, a greater resistance to oxidation is obtained than when the oxidation inhibitors 'are used-in 06njunction with a less-refined lubricating-hi1.

In attempting to increase the oxidation bility of transformers and turbine oils, kn oxidation inhibitors (such as the "dialkyl lenides of Denison and Condit Patents 2398;414 and 2,398,415) were incorporated therein, and, as expected, the resulting compounded oils "were more resistant to oxidation than the base oils containing no inhibitors. However, it was not to be expected that the oxidation stability f'of "the oil thus compounded with oxidation inhibitors could be increased still further by adding thereto an agent which by itself is not "an oxidation inhibitor. 7 I

It is an outstanding feature of this invention that the oxidation stability of "a lubricating bil compounded with an oxidation inhibitor is materially increased by adding thereto an {agent not known as an oxidation inhibitor which agent asserts synergistic eliects in combination with the oxidation inhibitors of this invention.

It is a primary object of this invention to produce lubricating oil compositions which are highly resistant to oxidation.

It is another object of this invention to incorpora'te in mineral oils containing oxidation inhibitors an agent exhibiting a marked synergistic cheat on certain oxidation inhibitors.

It is a further object of this invention to produce transformer oils and the like which are more resistant to oxidation than those heretofore known. I

These and other objects may be obtained from the disclosures and the claims noted hereinbelow.

It has been discovered that highly oxidation resistant compositions of oils of lubricating viscosity may be prepared by incorporating hydroxy anthraquinones in said compositions containing oxidation inhibitors, particularliselenides. H

The hydroxy anthraquino'nes of this invention are anthraquinones containing two hydroxyl groups on the ring, such as exemplified by alizarin (1,2-dihydroxy-anthraquinone), quinizarin (1,4-dihydroxy-anthraquinone) 1,5-dihydroxyanthraquinone and 1,8-dihydroxyanthraquinone. It is preferred to use dihydroxy anthraquinones particularly, quinizarin.

Oxidation inhibitors which are contemplated by this invention to be used in viscous oil compositions in combination with hydroxy-anthraquinones include selenides. lhe particular selenides of the present invention may be represented by the formula:

wherein A is R1, Se-Bz, M or a hydrogen atom, R, R1 and R2 are like or unlike substantiallyhydrocarbonaceous organo groups connected to selenium through an aliphatic carbon atom, at least R, and preferably also R1 and R2, contain at least carbon atoms, preferably 12 to carbon atoms, and M represents a cationic salt-forming radical, such as a metal atom. Thus, the selenides embrace di-organo monoand diselenides, selenomercaptans( organo hydroselenides) and selenomercaptiues (metallo organo selenides) Preferred are the di-organo selenides (i. e., R-Sen-- R", where n=1 or 2 and R and R are like or unlike aliphatic radicals each of at least 10 carbon atoms) of these, the monoselenides are ordinarily preferred.

Suitable organo groups, which are preferably hydrocarbon groups, include alkyl groups, such as decyl, lauryl, cetyl, etc., alkylated cycloaliphatic radicals, such as ethyl cyclohexyl, dimethyl cyclohexyl, etc., alkylated aralykyl radicals, such as cetylbenzyl, butylbenzyl, etc., and the aliphatic radicals derived from halogenated mixtures of hydrocarbons such as chlorinated naphtha, chlorinated kerosene, chlorinated parafiin wax, etc. The aliphatic groups man contain non-hydrocarbon substituents such as chlorinabromine, hydroxyl and amino so long as their essentially hydrocarbon character remains substantially unchanged. Of these various types of organo groups, the allayl radicals are preferred and of these, the dodecyl group is especially preferred.

The cationic salt-forming radical may be metals, such as sodium, calcium, barium, zinc, potassium, lithium, strontium, aluminum, lead, thallium, etc., or the ammonium radical. Preferably, the metalsare the polyvalent metals, especially those of Groups III), IV and VIII of the periodic table.

The following specific examples of selenides will further illustrate the selenium compounds of the present invention: dialkyl selenides, such as octyl decyl monoselenide, dilauryl monoselenide, dieicosyl monoselenide, dialkyl diselenides, such as didecyl diselenide, didodecyl diselenide (dilauryl diselenide) diheptadecyl diselenide, dieicosyl diselenide, selenomercaptans, such as lauryl selenomercaptan, cetyl selenomercaptan, octadecyl selenomercaptan, parafin wax selenomercaptan, etc., and the corresponding sodium, calcium, barium, zinc, cadmium and lead salts of such selenomercaptans.

Suitable. base 0115 include a wide variety of lubricating oils such as naphthenic base, parafiin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oil derived from coal products, and synthetic oils,,e. g., alkylene polymers (such as polymers of propylene, butylene, etc., and mixtures thereof), alkylene oxidetype polymers, dicarboxylic acid esters and liquid esters of acids of phosphorus. Synthetic oils of the alkylene oxide-type polymer which may be used include those exemplified by the alkylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides, e. g., propylene oxide, in the presence of water or alcohols, e. g., ethyl alcohol, and esters of alkylene oxide-type polymers, e. g., acetylated propylene oxide polymers prepared by acetylating propylene oxide polymers containing hydroxyl groups.

Synthetic oils of the dicarboxylic acid ester type include those which are prepared by esterifying such dicarboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenyl succinic aci (such as those described in Moser Patents 2,124,628 and 2,133,734), fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, Z-ethyl-hexyl alcohol, dodecyl alcohol, etc. Examples of dicarboxylic acid ester synthetic oils include dibutyl adipate, dihexyl adipate, di-Z-ethyl-hexyl sebacate, di-n-hexyl fumarate polymer, etc.

Synthetic oils of the type of liquid esters of acids of phosphorus include the esters of phosphoric acid, e. g., tricresyl phosphate; the esters of phosphonic acid, e. g., diethyl ester of decane phosphonic acid.

Other suitable phosphonic acid esters may be obtained by the process described in Jensen and Clayton application Serial No.86,856 filed April 11,

19 19, now abandoned, according to which process hydrocarbons containing at least one aliphatic carbon atom. are exposed simultaneously to the action of phosphorus trichloride and an oxygencontaining gas to produce hydrocarbon phosphonyl chlorides which may be converted to the desired esters, such as reacting the allryl phosphonyl chloride with hydroxyl-containing compounds such as phenols and aliphatic alcohols 01' with olefin oxides such as propylene oxide or the like.

The oxidation inhibitors (i. e., the organic selenium compounds) which are present in the lubricating oil composition may be present in amounts from'about 0.0001% to about 5% by weight of the final composition, that is, an amount sufficient to increase the resistance of the lubrieating oil composition to oxidation. It is preferred to use from about 0. 1% to about 2.0%.

The hydroxyanthraquinones of this invention (e. g., quinizarin) may be present in the final mineral oil composition in amounts from about 0.0001% to about 1.0% by weight of the final composition. It is preferred to use an amount sufficient to enhance the oxidation-inhibiting characteristics of the organic selenium compound, preferably from about 0.02% to about 0.1%.

The organic selenium compound may be replaced in part by alkylated phenol oxidation inhibitors, such as 2,6-di-tertiary butyl--methyl phenol, to procure a long life for the compounded oil. This is desirable since it provides a way of cutting down the amount of expensive selenide without reducing the'long life as obtainable with selenides alone. Thus, 'a' hydroxyanthraquinone (e. g., quinizarin) may be added to a lubricating oil containing an alkylated phenol oxidation inhibitor (e. g., 2,6 di tertiary butyl 4 methyl phenol) and a selenide oxidation inhibitor (e. g., dilauryl monoselenide) to obtain a long life for the compounded oil.

A remarkable featureof this invention is the Wholly unexpected, greatly enhanced synergisticeffects which are obtained between lubricating oil oxidation inhibitors (e. g., organic selenium compounds) and the hydroxy anthraquinones (e. g.,

awe-ntfq'uinizarin): 'Nowhere-wouidany one-expect to find such synergistic 'efiects as disclosedhereinby the additibnof-a- 'hydroxyanthraquinone as' 'a seeondary-agent'toa lubricatingoircomposition con taining additives which are known to inhibit oxi-e dation, particuiarly' to find its. anti-oxidation properties enhanced so tremendously by the addition of a secondary agent which in itself has relatively no effectinhibiting oxidation in a lubricating oil. Obviously, it is not merely-an ad- 'ditive' effect which is-"obtained between the combinations ofthe known oxidation inhibitor in the lubricating oil and the hydroxyanthraquinones because the hydroxyanthraquinones in themselves are practically ineffective in inhibitin the oxidation in the lubricating oil composition. 7

In the tables hereinbelow, data are presented to show the synergistic efl ects obtained by testing the compositions of additives in a lubricating oil I, under severe conditions. In order to test effectively the compositions of. this invention, a more drastic test was devised than is normally used in evaluating transformer oilsv and the like. This test has been called the California Research Transformer Oil'StabiIity Test. The testis ru-n as follows: I

A 300-gram sample to be tested is placed in a glass tube which is set in an oil bath at 250 F. Oxidation catalysts, i. e., 112 /2 square centimeters of medium silicon transformer iron (such as USS Trancor 72) and 450 square centimeters of No. 14 gauge ASTM electrolytic copper wire are inserted in the tube. Oxygen is bubbled through the test sample at the rate of 3 liters per hour until the test sample has an acid number of 1:0 (milligrams of KOH per gram sample of oil). The number of hours required for the sample to show an acid number of 1.0 is known as the test life of the sample.

The data presented in the following tables will serve to illustrate the nature of the results that were obtained in accordance with the present invention.

Table I.Quiniza1'in in a mineral oil containing dilauryl selenide 'lest No.

Quiuizarin 1 Base Oil 24 l A California solvent-refined parafiiuic base oil having a viscosity of 58 SSU at 100 F., and having 90% unsulfonatable residue.

1 The base oil of (1) which had been treated further to yield an oil having 95% unsulionatable residue.

3 The base oil of (l) which had been treated further to yield an oil having 98% unsulfonatable residue.

Table II hereinbelow presents data on the re sults obtained by replacing in part and in toto dilauryl selenide (in a lubricatin oil composition containing quinizarin) with 2,6-di-tertiary butyl- 4-methyl phenol.

Additive (Percent by Weight) 2;6-Diter- Test Life Dil'aui'yi: ti'ary- Home) Mono- Butyl-4- Mm selenide Methyl Phenol l4 Base om... 24 15.. .do. o. 05 25 16-. .doJ 1o 1 365 310 490 24 95 20 325 24 20 175 400 l A California solvent-refined peraflinic base oil having a viscosity of 58 SSU at 100 F., and having unsulionatable residue.

. The bascoil 05 (l) which had been treated further to. yield an oil having 'unsulfonatab'le residue.

3 The base. oil of (l) which had been treated further to yield oil having 98% unsulfcuatable residue.

The data of above Table II show that the test life of a lubricating oil containing a dialkyl monoselenide oxidation inhibitor and an alkylated phenol oxidation inhibitor is remarkably increased by incorporating therein a hydroxyanthraquinone. These data show that the combination of a hydroxyanthraquinone (e. g., quinizarin), a selenide oxidation inhibitor (e. g., dilauryl monoselenide), and an alkylated phenol oxidation inhibitor (e. g., 2,6-di-tertiary butyl-4-methyl phenol) in a lubricating oil exhibits a remarkable synergistic effect to enhance the anti-oxidation characteristics of the lubricating oil composition.

In some instances, 2,6-di-tertiary butylimethyl phenol and similar alkylated phenol oxidation inhibitors may replace in toto the selenide oxidation inhibitor. That is, a hydroxy anthraquinone (e. g., quinizarin) may be added to a lubricating oil containing an alkylated phenol oxidation inhibitor (e. g., 2,6-ditertiary butyl- 4-methyl phenol) to produce synergistic effects in prolonging the life of a lubricating oil composition.

Organo-tin compounds, such as tetraphenyl tin, are also eiiective to replace, in part, a portion of the organic selenium compounds (e. g., dilauryl monoselenide) which is present in a lubricating oil in combination with a hydroxyanthraquinone (e. g., quinizarin). Furthermore, a hydroxyanthraquinone is effective for increasing the life of a lubricating oil containing an alkylated phenol oxidation inhibitor (e. g., 2,6-di-tertiary butyl-4-methyl phenol) in combination with an organo-tin compound (e. g., tetraphenyl tin). For example, when 0.1% by weight of 2,6-ditertiary butyl-4-methyl phenol and 0.06% by weight of tetraphenyl tin are incorporated in a California solvent-refined parafiinic base oil having a viscosity of 58 SSU at 100 F. containing 0.05% quinizarin, the life of the base oil was increased from 24 hours to greater than 1000 hours.

The combination of additives of the present invention may be used effectively in oils generally, whether hydrocarbon or, non-hydrocarbon, although their present fieldof chief utility is in transformer oils and in turbine oils. The hydroxy-anthraquinones may also be used in oils containing other groups of additives in addition to anti-oxidants. For example, in addition to the above-noted compounds, the lubricating oils may contain other agents, such as pour point depressants, oiliness agents, extreme pressure agents, blooming agents, compounds for enhancing the viscosity index of the hydrocarbon oil, greaseforming agents, peptizing agents, etc.

We claim:

1. A transformer oil composition consisting essentially of a major portion of an oil of lubricating viscosity and from about 0.0001% to about 5%, by weight, of a dialkyl monoselenide containing from 12 to 30 carbon atoms in each alkyl group, to which transformer oil composition is added from about 0.000% to about 1.0%, by weight, of a hydroxy anthraquinone selected from the group consisting of 1,2-dihydroxy-anthraquinone; 1,-dihydroxy-anthraquinone; 1,5- dihydroxy-anthraquinone and 1,8-dihydroxyanthraquinone.

2. A transformer oil composition consisting essentially of a major portion of an oil of lubricating viscosity and from about 0.1% to about 2.0%,

by weight, of a dialkyl monoselenide containing from about 12 to 30 carbon atoms in each alkyl group, to which transformer oil composition is added from about 0.02% to about 1.0%, by weight,

8 of a hydroxy anthraquinone selected from the group consisting of 1,2 dihydroxy anthra quinone; 1,4-dihydroxy-anthraquinone; 1,5-dihydroxy-anthraquinone and 1,.8-dihydroxy-anthraquinone.

3. The transformer oil composition of claim 1, wherein said oil is a petroleum lubricating oil.

4. The transformer oil composition of claim 1, wherein the dialkyl monoselenide is di-lauryl monoselenide.

5. The transformer oil composition of claim 1, wherein the dihydroxy-anthraquinone is quinizarin.

WILLIAM T. STEWART. CHARLES D. NEWNAN. NEAL W. FURBY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,016,648 Orelup Oct. 8, 1935 2,053,421 Burk et al. Sept. 8, 1936 2,214,443 Varteressian Sept. 10, 1940 2,225,533 Dewey Dec. 17,. 1940 2,261,888 Rocchini Nov. 4, 1941 2,398,415 Denison et a1 Apr. 16, 1946, 

1. A TRANSFORMER OIL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PORTION OF AN OIL OF LUBRICATING VISCOSITY AND FROM ABOUT 0.0001% TO ABOUT 5%, BY WEIGHT, OF A DIALKYL MONOSELENIDE CONTAINING FROM 12 TO 30 CARBON ATOMS IN EACH ALKYL GROUP, TO WHICH TRANSFORMER OIL COMPOSITION IS ADDED FROM ABOUT 0.000% TO ABOUT 1.0%, BY WEIGHT, OF A HYDROXY ANTHRAQUINONE SELECTED FROM THE GROUP CONSISTING OF 1,2-DIHYDROXY-ANTHRAQUINONE; 1,4-DIHYDROXY-ANTHRAQ@UINONE; 1,5DIHYDROXHY-ANTHRAQUINONE AND 1,8-DIHYDROXYANTHRAQUINONE. 